I'm not sure. He also got a lot wrong. Here's a response from an environmental scientist that specializes in nuclear waste disposal[0]. Honestly that episode caused me to be more critical of him. Of course it is always easy to fall victim to the Murray Gellman effect, but we should try our best not to and if some authoritative source is incorrectly characterizing a field you're intimately familiar with, you should be more careful with that source in the future. I mean he is a comedian first and foremost and the conclusion does essentially come down to "experts are dumb" which is a little insane to hear and rather insulting. Especially with a topic that is extremely complex and difficult to understand.
[0] https://www.forbes.com/sites/jamesconca/2017/08/24/please-jo...
If John Oliver dedicates a whole episode to that problem, it is kinda a big of a deal, isn't it?
Leave it in the ground. WWS is sufficient to transform our energy systems.